Method of manufacture of a flow element or pulsation dampener



March 10, 1964 G. H. MILLAR 3,123,900

METHOD OF MANUFACTURE OF A FLOW ELEMENT 0R PULSATIQN DAMPENER Filed July29, 1959 2 Sheets-Sheet l 60200 H. M/uAe mmvrox i 7 BY 20L: 30:4 11144 AOEA/EYS G. H. MILLAR 3,123,900

DAMPENER 2 Sheets-Sheet 2 b2 0 0 4 E W: 0 /9 9 v, 2 M 4/ 9 W i o m M 4 m5 r NYE 1. m W m 1 N A w E o G March 10, 1964 METHOD OF MANUFACTURE OF AFLOW ELEMENT OR PULSATION Filed July 29, 1959 United States Patent Thisinvention relates to improvements in a method of making an instrumentfor measuring a characteristic of a flowing fluid, a flow meteringelement and/or pulsation dampcner for said instrument, and/or method ofmanufacture of said flow element, and relates more particularly to astructure wherein this flow element is constructed to provide theadvantages of laminar flow.

An object of the present invention is to provide a method of making aninstrument for measuring a characteristic of a flowing fluid, or anelement used in said instrument, wherein the element is characterized bythe linear relationship it provides between the differential pressurethereacross and the volume or velocity of fluid flow therethrough, itslarge range of flow operation, mechanical rigidity, geometric integrityof form, constant calibration for instrument accuracy, assurance oflaminar flow, locking of its components against relative movement duringhandling, uniform size of all its flow passageways, unobstructedcondition of its flow passageways, thin wall portions forming the flowpassageways so that the element has maximum porosity, accuracy withpulsating flow, calibration unaffected by absolute pressure of theflowing fluid, calibration aifected in a predictable way by temperaturechange in the flowing fluid, and/0r easy to clean construction.

A further object of the present invention is to provide a method ofmaking a flow element adapted to be arranged in modular construction ineither series or parallel arrangement.

A further object of the present invention is to provide a method ofmaking a plurality of flow elements arranged in series with gapstherebetween having pressure taps to a differential pressure measuringinstrument with this construction having the advantage of impact orturbulence reduction, pressure averaging, and/or increased porosity tominimize velocity change into or out of one of the flow elements.

A further object of the present invention is to provide a method ofmanufacturing a flow element with permanent mechanical rigidity,geometric integrity of form, generally uniformly sized and unobstructedpassageways, maximum porosity, and/or many parallel passageways eachwith small hydraulic diameter to assure laminar flow.

A further object of the present invention is to provide a method ofmaking a structure comprising a flow element characterized by itsmechanical permanence, geometric integrity, permanent rigidity,permanence of calibration, easily cleaned and handled constructionwithout change of calibration, laminar flow characteristic, minimumreduction in flow area while providing laminar flow, inexpensivemanufacturing cost, ease of assembly, structural simplicity, strong andsturdy nature, ease of operation or use, and/or low operating cost.

Other objects and advantages of this invention will be appa'ent from theaccompanying drawings and description and the essential features will beset forth in the appended claims.

In the drawings,

FIG. 1 is a longitudinal sectional view through one form of fluidcharacteristic measuring intrument with the hereinafter described flowmetering element therein;

FIG. 2 is a longitudinal sectional view through another 2 form of fluidcharacteristic measuring instrument with an exterior view of the flowmetering element therein;

FIG. 3 is a longitudinal sectional view through a third form of thefluid flow characteristic measuring instrument with the flow meteringelements shown in side elevational View, being modular in form, andarranged in series;

FIG. 4 is a side elevational View of the flow metering element shown inFIGS. 1, 2 and 3;

FIG. 5 is an end view of the flow metering element in FIG. 4 with thesize of the passageways and spaces in the helix enlarged for clarity ofillustration;

FIG. 6 is an enlargement of the peripheral portion of the helix in FIG5;

FIG. '7 is a perspective View of two sheets before spiral winding intothe element in FIG. 5;

FIG. 8 is a vertical sectional view taken along any of the lines 8i inFIGS. 1, 2 and 3;

FIG. 9 is schematic side elevational view of a vibrator with a flatvibrator plate therein supporting the flow element herein during themanufacture of the fiow element; while FIG. 10 is a vertical sectional,schematic view of a brazing furnace having therein the flow elementduring flow element manufacture.

Before the apparatus and method here illustrated and described isspecifically described, it is to be understood that the invention hereinvolved is not limited to the structural details, method steps, orarrangement of parts here shown since an apparatus or method embodyingthe present invention may take various forms. It also is to beunderstood that the phraseology or terminology herein employed is forpurposes of description and not of limitation since the scope of thepresent invention is denoted by the appended claims.

Those familiar with this art will recognize that the present inventionmay be applied in many ways, but it has been chosen to illustrate thesame as an instrument for measuring a characteristic of a flowing fluid.The herein described characteristic is that of a gas but it should bereadily understood that any of the instruments described herein may beused: (1) to measure the characteristic of any suitable fluid, eithergas or liquid, under many conditions, and (2) to measure othercharacteristics of a flowing fluid besides flow or velocity, such asviscosity of the flowing fluid, temperature change, pressure drop, etc.Also some aspects of the disclosed invention may be useable with otherhow metering elements of passageway or orifice type instead of onlyelements 1% disclosed herein.

FIGS. 1, 2 and 3 disclose three different forms of instruments utilizingone or more flow metering elements 10. Each includes housing 26, 30 or4t? having cylindrical sleeve 2%, 3% or dill) respe ti ely having bore20a, Etla or 4% through which fluid flows in fluid flow direction 12with the instruments adapted for measuring a characteristic of thisflowing fluid. In FIG. 1, two end adapters 22 are detachably screwedinto opposite ends of sleeve 2-521) and are detachably connected bythreads to inlet pipe 23% and outlet pipe 2 5. in FIGS. 2 and 3,housings 3d and 49 respectively have inner sleeves 3d!) and 46bsupported by one or more solid, annular adapter rings 3g and 49g withincylindrical outer sleeves Stir: and itllz preventing fluid flow betweens1 eves Sub, 36th and iib, 4%.

In each instrument, any suitable pressure differential measuringinstrument may be used, such as manometer 14 containing any suitablemanometer liquid 13 and connected to upstream tap 15 and downstream tap16 from bore 20a, Sila or A da. Each of these taps includes adaptersleeve 17 welded to the outer surface of housing 26, or and bore 2dr,3th or 4th through housing sleeve 2%, 30/1 or 40h into bore 20a, Ella ordila. Fitting 18 is screwed into each adapter sleeve 17. Suitable flexi-3 ble tube 19 is telescoped over each fitting 13 and leg of manometer 14so that fluid pressure from each tap 15 or 7.6 will be directed againstthe surface of manometer liquid 13 in each manometer leg. Althoughsleeve 17 and fitting 18 may be used alone without the parts shown inFIG. 8 therein to obtain some advantages of the invention, it ispreferred that they include the parts shown as gland helical spring 80,ring-like gland 81, O-ring 82, and pulsation dampening plug or member 83of any suitable porous material. It should be apparent that plug 83 isalso useable in other type pressure measure instruments.

In FIGS. 1, 2 and 3, the flow metering elements extend across the bores28a, 36a and 4041. One element 10 in FIGS. 1 and 2 and three elementsit) in PEG. 3 are located along the flow direction 12 between taps and16. As will be apparent hereinafter, element 10 has a plurality of fluidflow passageways 19a extending through this flow element in the flowdirection 12 with each pas sageway having a hydraulic diametersufiiciently small for assuring laminar flow of the fluid within therange of operation of the element.

Fluid flow may be either laminar or turbulent flow. Laminar flow ischaracterized by fluid flow with a Reynolds number below 2000. Theimportant difference between laminar and turbulent flow is that forlaminar flow the differential pressure is linearly related to thevelocity or fluid flow volume of the flowing fluid, whereas, forturbulent flow the differential pressure is related to the square of thevelocity or fluid flow volume of the flowing fluid.

Hence, the differential pressure of the flow at turbulent velocity inhousing bore 20a, 30a or 49a in FIGS. 1, 2 and 3 with elements 10omitted would be the same as the flow through any single flow orifice soas to be related to the square of the velocity or fluid flow volume ofthe flowing fluid because turbulent flow would be existing. Whenelements 10 are inserted, the many passageways 10a in FIG. 5 in eachflow element or elements 10 convert the turbulent flow in each housingbore into laminar flow for measuring purposes. Then, as long as the flowthrough elements 10 in FIGS. 1, 2 and 3 in the direction of flow 12 islaminar, the differential pressures measured on manometers 14 will belinearly related, directed related, or proportionally related to thevelocities or fluid flow volumes.

Element 10 depends for its principles of operation on capillary flow.This may be stated as a mathematical law, known as Poisseuilles law,which relates the volume of fluid flow through a capillary tube to theditferential pressure, the diameter of the tube, the length of the tube,and the absolute viscosity of the flowing fluid. This law may beexpressed as:

where Q is the volume flow, K is the constant dependent on units, P isthe differential pressure, v is the absolute viscosity, D is thehydraulic diameter, and L is the length of capillary passageway. Thisequation is valid only: (1) for laminar flows, namely flows havingReynolds numbers below 2000, and (2) for design configurations in whichthere is no velocity change into or out of the capillary section.Reynolds number is a dimensionless parameter of fluid flow used as ayardstick to determine if the state of the flowing fluid is laminar orturbulent. Reynolds number may be expressed by the mathematicalequation:

DV d

stallation of element it) will cause laminar flow. The large diametricalsize of any of tne bores 20a, 30a or 40a Without an element 10 thereinwill be sufficiently large in diameter that the Reynolds number may beabove 2000 so turbulent flow will exist. Installing an element 10 willcreate laminar flow because the element provides many pasageways 10a,each of which has a uniform hydraulic diameter as small as practical. Itis this reduction in diameter of flow passageways which brings theReynolds number below 2000 and creates laminar flow in passageways 10a.Laminar flow is characterized by streamlines of flowing fluid in thepassageways lfla and a parabolic distribution of velocity across eachpassageway. Actually, in laminar flow the first lamina or layer of fluidnext to the wall of each passageway does not move so that any roughness,dirt or corrosion thereon does not affect the relationship except asthey alter the cross sectional flow area. In contrast, in turbulent flowthere are cross-currents and intermixing of the flow streams with aresulting scrubbing action on the walls of the pipe which allows piperoughness to interfere with the flow and affect the flow relationshipsmeasured by manometer 14.

Element 10 is shown in detail in FIGS. 4, 5 and 6.

Although element 10 may be manufactured in any suitable manner, apreferred method of making this laminar flow element 10 include one ormore of the numbered steps described hereinafter.

First, two sheets 50 and 52 are selected with each being ofsubstantially uniform width dimension 51 and being made of any suitablematerial with each of these sheets being planar in form, as shown bysheet 50 in FIG. 7, at this stage of manufacture. It has been found thatsatisfactory rcsults are obtained when each sheet is a thin sheet ofmetallic material, such as 302 stainless steel, having a full temper ofmaximum hardness (about 42 Rockwell C in the as-rolled condition) so asto be easier to handle, to form, and to get the end results even thougheach sheet may be very thin. A thickness dimension of not substantiallygreater than 0.001 inch has been found to give satisifactory results, aswill be more apparent hereinafter.

Second, sheet 52, being of planar form like sheet 50 in FIG. 7, is nowuniformly corrugated so sheets 50 and 52 have the appearance shown inFIG. 7. This sheet 52 is run through crimping rolls or dies with thestraight line, generating elements 52a of the corrugations extendingparallel to each other, to the flow direction 12 in FIGS. 1-3, and tothe longitudinal axis 10d and axis 10 of the spiral in the finishedelement 10 in FIGS. 4 and 5. Each corrugation has peak 520 and valley52b.

Third, sheets 50 and 52 are superimposed in contact so that the widthdimension 51 in FIG. 7 generally coincide and the lengths of the sheets50 and 52 are substantially the same so that the sheets aresubstantially coextensive. It should be noted that this width dimension51 in FIG. 7 becomes the length dimension 51 of the element 10 in FIG.4.

Fourth, the superimposed sheets 50 and 52 are spirally wound withgenerally uniform tension about metallic core 54 into the form shown inFIG. 5 with the generating elements 52a of the corrugations extendingparallel to the axis 10d of this spiral. Then, most of the portions ofcorrugated sheet 52 are sandwiched between portions of sheet 50, asshown in FIG. 6, with corrugation peak 520 and valley 52b generally incontact with sheet 50.

Fifth, helically wound sheets 50 and 52 are telescopically inserted withcore 54 into cylindrical sleeve cover or shell 56 made of suitablemetallic material. The rigid, cylindrical bore of metallic casing 56retains sheets 50 and 52 in the spirally wound condition in spite of thefull temper of the material of these sheets tending to straighten themto the form shown in FIG. 7. The interlocking spiral shape of sheets 50and 52 in FIG. 5 provides a plurality of element Wall portions 10c bysheets 50 and 52 defining many small flow passageways 10a with eachlocated between a corrugation of sheet 52 and a portion of the sheet 50.The cylindrical shell 56 serves to connect these wall portions 150together in the form shown in FIG. 5.

Sixth, it may be desirable under some circumstances to vibrate theassembly shown in FIG. so as to align the sheets 50 and 52 and controlthe shape of the flow passageways a therebetween. If one spiral face,such as element end 102:, is placed downwardly on a vertically vibratingflat plate 91 (shown schematically in FIG. 9) of any suitable typedriven by any suitable vibrator 92 (shown schematically in FIG. 9), thevertically vibrating plate 91 will vibrate the flow element along theaxis 10d of the spiral so as: (1) make all the width dimensions 51 inFIG. 7 of sheets 50 and 52 laterally coincide so that element 10 will beof uniform length 51 with the end faces thereof, such as end 10b, eachplanar and parallel to each other, and (2) equalize by the vibration anystrain developed during winding of the sheets into the spiral so thatthe passageways 10a will be of substantially uniform size.

Seventh, the components of element 10 are given mechanical permanence ofform by suitable connecting means connecting these wall portions 100together. Here, each corrugation peak 520 and each corrugation valley 5%of sheet 52, or at least as many as possible, is secured at contact 58to plate 50 and the surface of core 54 and/ or shell 56; and sheet 50 issecured at contact 58 to the surface of core 54 and/ or shell 56. Thissecuring or joining is by metallic heat fusion at contact by heating theassembly in a furnace in any suitable manner.

Here are two alternative methods of metallic heat fusion. First, brazingmay be used to provide the joining by heat fusion, Then, a suitablebrazing material is applied to sheets 50 and 52 at any desirable stagein manufacture, and then the assembly in FIG. 5 may be heated in asuitable hydrogen atmosphere brazing furnace 94, shown schematically inFIG. 10, to a brazing temperature for sufficient time for causing fusionto join together the component parts at contacts 58. Satisfactoryresults have been obtained with a conventional brazing compound withheating four hours at a temperature of 2000 F. To be sure that thebrazing material does not clog the small passageways 10a, it isdesirable that axis 10d be located vertically during heating, as shownin FIG. 10, so that the brazing material will run, if any fiow takesplace, longitudinally of these flow passageways. Second, another methodof metallic heat fusion assures a clean bond at contacts 50 with nochance of blocking the flow passageways 10a. Here, the surfaces ofsheets 50 and 52, core 54, and shell 56 are cleaned before assembly, andthen the assembly in FIG. 5 is heated in a furnace, preferably ahydrogen atmosphere furnace, to near the melting point of the materialof at least one of the sheets, so that the material is fused withmolecular fusion occurring to form the bond at contacts 58. Thistemperature is the eutectic point of the material. Sheets 50 and 52,core 54 and shell 56 are preferably made of the same material, such as302 stainless steel, so all will fuse together. Then, this temperaturemay be about 2250 F. for these sheets, core and shell. This secondfusion method and this last described construction are the preferredform. The dew point for the hydrogen atmosphere should be minus 40 F.

In either of the two metallic heat fusing methods mentioned in thepreceding paragraph, certain advantages are obtained. The completedelement 10 has many advantages desirable in a flow metering element, aswill be readily apparent from the description herein, First, this heatfusion provides an intermolecular and intermetallic bond by heat fusingtogether sheets 50 and 52, core 54, and shell 55 to provide a single,mechanically rigid, geometric structure forevermore maintainingdimensional integrity and permanence of form. Second, since securementbetween the component parts is at contacts 58, each passageway 10a isunobstructed and not partially or completely bloc ted by any securingmeans for these sheets 50 and 52. Hence, laminar flow will exist in eachflow passageway and no partial obstruction exists in any passageways toincrease the velocity to the turbulent flow range to affect themeasuring by manometer 1d. Third, heating of the assembly in FIG. 5 notonly fuses and joins the components thereof at contacts 53 but alsorelieves stresses by annealing so as to relieve the stresses caused bythe full temper of sheets 50 and 52 and by the step of spirally windingthese sheets. This stress relieving more readily assures mechanicalstructural permanence of form and uniform size of each flow passageway10a, so as to assure that the metering element 10 will maintain itscalibration and that laminar flow will exist in each flow passageway. Itshould be noted that the vibration in the aforementioned sixth step alsorelieves stresses to provide some of these advantages.

Now, it should be apparent that each passageway 10a of element 19 has asubstantially equal hydraulic diameter, has dimensional rigidity, and issubstantially unobstructed so that the metering calibration of element10 is maintained and laminar flow will take place in each passageway.The equal sizes of the passageways are assured by the unformcorrugations formed in sheet 52, the substantially uni-form tension usedduring winding the helix, and the annealing or stress relieving by heat.Also, the thinness of each sheet 51} or 52, as shown by dimension 60 inFIG. 6, increases the porsity of element 10 and permits the use of asmall hydraulic radius for each passageway 10a. Therefore, element 10meets both conditions previously mentioned as being required for theformula under Poisseuilles law. These conditions are that the flow is inthe laminar flow range, and that the structural configuration is suchthat there is substantially no velocity change into or out of thecapillary sections provided by passageways 10a. In other words, thethinness of dimension 60 approaches zero toward the desired percentporosity. As mentioned before, the full temper permits these thin sheetsto be properly handled in manufacture, crimped, and spirally wound.Element 10 with the following dimensions has been found to givedesirable results. Each passageway 10a in FIG. 6 is generally triangularin cross section with each altitude 61 of each equilateral triangle nogreater than 0.020 inch and preferably as small as 0.012. inch, and withthe thickness dimension as of each wall portion 100 being less than0.0015 inch and as small as 0.0005 inch if possible but preferably notsubstantially greater than 0.001 inch.

Although the preferred form has been described, it should be readilyapparent that variations in structure come within the scope of theinvention although all of the advantages mentioned heretofore may not beobtained. First, the components of element 10 may not be fused at allcontact points 58 but at a sufficient number to give a mechanicalpermanence of form. Second, sheets 50 and 52 may not be fused to bothcore 54 and shell 56 if so desired.

Now, it should be readily apparent that the instruments in FIGS. 1, 2and 3 will each measure the velocity or flow volume of the fluid movingin flow direction 1?, as a linear relationship of the pressure dropacross one or more of these elements 10 with this differential pressureindicated by the vertical dimension 6 between the tops of the legs inmanometer 14. These instruments will measure properly as long as laminarflow exists in elements 10.

The construction of flow elements 10 readily lend them to modularconstruction and arrangement. These elements 10 may be arranged inseries or in parallel to increase instrument readability or increasevolume how if so desired. In either series or parallel, at least onehalf the fluid flow will go through each of the elements to change thecalibration of the instrument. For example, three elements Jill arearranged in series in FIG. 10 between taps 15 and 16 with sleeve ihbbeing of suflicient length so that all three of these elements areconnected in series in its bore t'da. If only one element 1% is locatedin bore 4tia, a typical installation might provide a one inchdifferential height dimension 64 of liquid 13 in manometer 14 for onecubic foot per minute of air flowing in direction 12 with this singleelement 19 providing one square inch of flow area and being three incheslong in axial dimension. Then, if three elements 10 were arranged inseries, as shown in FIG. 3, the assembly is lengthened to nine inches,and one cubic foot per minute of air will cause differential pressuredimension 64 to be three inches. If two of these elements were used andarranged in parallel instead of series, the flow area would be increasedto two square inches so that two cubic feet per minute of air wouldcause differential pressure dimension 64 to be one inch. Hence, thelinear relationship still is maintained.

In some installations, the Fl. 1 construction may be desirable. FIG. 1discloses two other flow elements 7% and 71 of the same cross sectionalpassageway construction (as seen in FIG. as the aforedescribed fiowelement it} with these other flow elements 7%) and 71 straddling elementIt} in flow direction 12 with taps 15 and 16 in fluid communication withthe spaces 72 and 73 between each adjacent pair of these elements 19, 7tand 1t 71. Upstream element 70 is located on the opposite side of tap 15from element It), and downstream element 71 is located on the oppositeside of tap 16 from element ltl. This construction has severaladvantages including: (1) reducing the velocity affects of the fluidstream entering and leaving element so as to provide a more linearcalibration by assuring laminar flow in element It), (2)-reducingextreme turbulence, 3) assuring that no upstream or downstream run ofpipe is required to assure laminar flow because impact reducers 7t} and'71 permit element 10 to be connected directly in a line to an elbow orother abrupt pipe fitting, 4) providing in each space 72 or 73 apressure averaging function by single tap or 16 instead of requ rrngaplurality of circumferentially arranged taps required in a ringpiezometer for pressure averaging, and (5) minimizing the fluid velocitychange into and out of element ill by forcing the fluid to assumegenerally the same path of travel through elements 7t? and 71 as 1ttaltes through element it so as to satisfy the aforementioned secondcondition for making Poisseuilles law and formula valid by minimizingthe velocity change into and out of element It and by minimizing any uErof 100 percent porosity in element It). Elements 7t) and 71 may be ofshorter axial length, as shown in FIG. 1, while still having the samecross sectional shape shown in FIG. 5. Although the axial lengthdimension 75 in FIG. 1 of either space 72 or 73 may be of any suitablelength, the best results are obtained when this distance 75 along flowdirection 12 in fluid communication with tap 15 or to is notsubstantially greater than, and preferably being approximately equal to,the hydraulic radius of each flow passageway 10a. Then, each space 72and 73 will assure proper averaging of the pressure and laminar flow. Insome installations, both elements 70 and 71 may not be needed. Forexample, downstream element 71 could be eliminated where there is nodisturbance downstream from element 10, such as bore 23a has a long rundownstream from element 10.

Here are some of the advantages of the use of element 10:

First, with laminar flow, a linear relationship exists betweendifferential pressure and the flow volume or velocity.

Second, element 10 will operate over a larger flow ratio that a sharpedges orifice with no loss in readability. For example, element 10 maybe used over a {-3 flow ratio of 10:1 while an orifice is generallyconsidered to be applicable only over a flow ratio of 3:1.

Third, ele'nent it has several outstanding features especially adaptingit for use in a flow measuring instrument. Element iii has built inpermanent mechanical rigid ty and geometric integrity of form so thatthe calibration of element It? emains constant for instrument accuracy,and laminar flow is always assured because the components of element 15)do not change their relative positions and the flow passageways 19:: donot change sizes during cleaning or handling. Element it) obtains itsmechanical rigidity and geometric integrity by its ingle, fused,mechanical construction instead of depending on friction, mechanicalassembly, or other types of fabrication which may permit relativemovement of the components during handling. Each flow pasageway 16a isof uniform size and is unobstructed so that element 10 has throughoutits flow range laminar flow and a constant calibration. Wall portionshave a thickness dimension 6% in FIG. 6 of minimum size so as toincrease p0- rosity of element It and to minimize velocity change intoand out of each of the capillary sections or passageways 19a of elementAl. Also, the hydraulic diameter of each passageway 19a is of minimumsize so that the Reynolds number will still remain in the laminar flowrange at higher flow velocities. Hence, the illustrated constructionassures that laminar flow will take place with the Reynolds number belowZOGO even though the velocity of flow is high because the hydraulicdiameter is small, and assures that the aforementioned two conditionsare met so that the formula in Poisseuilles law will apply.

Fourth, laminar flow element 1% is considerably less affected bypulsations in the flowing fluid than orifice plates or other meteringdevices which work on a squareroot curve. It manometer 14 is welldamped, it will indicate the arithmetic average of pressure pulsations,and especially when the pulsations are rapid with respect to the timeconstant of the manometer. An orifice requires a root mean-squareaverage of the differential pressure pulsations to give a trueindication of average flow. Only complex, electronic, differentialpressure measuring instruments can be adjusted to give aroot-mean-square average of pulsating differential pressure. Laminarflow element 19 requires manometer 14 to indicate the arithmetic averageof the pressure pulsations. Hence, element it) lends itself particularlywell to pulsating flow application, and generally a true average flowwill be indicated by the combination of an element It and a well dampedliquid column manometer 14, as shown in FIGS. 1, 2 or 3. Good dampeningor attenuation of the pulsations is obtained by pulsation dampeningplugs 33 in FIG. 8 in both taps 15 and 16 with this attenuation beingviscous in nature. Each plug 83 is preferably a sintered bronze plugwith 500 mesh or smaller opening size and with sufficient axial lengthto provide desired viscous attenuation of any pressure pulsations.Sintered bronze has the advantage over felt material of providingcontrolled and uniform porosity to provide uniform dampening.

Fifth, elements 1% are easily removed from bore 23a, 3% or 419a; easilycleaned; and easily maintained. Cleaning is desirable because thepassageways 10a are small and may become partially clogged during use.

Sixth, calibration of element 10 is unaffected by changes in absolutepressure of the flowing fluid because of the linear relationship.However, although the volume of flow will remain the same, a differenceof the fluid will mean that a difference in fluid weight is ilowin g.

Seventh, the flow of gas through element 19 is affected in a predictableway (desirable in a measuring instrument) by the temperature of theflowing gas. Gases, unlike liquids, show an increase in absoluteviscosity with an increase in gas temperature. The differential pressurefor a given volume of flow will increase under the formula inPoisseuilles law as the viscosity of the flowing gas increases.Therefore, for a constant differential pressure,

the flow through element will decrease as the temperature of the flowinggas increases. Hence, temperature correction curves can be provided forelements 10 with the characteristics of the curves being identical.

Eighth, element 10 may be used in a direct reading viscometer. Then,laminar flow element 10 is connected in series with a sharp edgedorifice through both of which flows the fluid in flow direction 12. Theorifice, unlike the laminar flow element 10, is unaffected by viscosity.At a pre-set flow condition, which is a pre-set differential pressureacross the orifice, the differential pressure across the laminar flowelement 10 is a direct measure of the viscosity of the flowing gas.Although this structure is not illustrated in the drawings, it should bereadily apparent to one skilled in the art.

Various changes in details and arrangement of parts can be made by oneskilled in the art without departing from either the spirit of thisinvention or the scope of the appended claims.

What is claimed is:

1. A method of making a laminar flow element, comprising superimposingin contact two substantially coextensive sheets of metal comprising afirst sheet of planar metal and a second sheet of uniformly corrugatedmetal, spirally winding said superimposed sheets into a laminar flowelement with the generating elements of the corrugations extendingparallel to each other and to the axis of said spiral with a flowpasageway located between each corrugation and said first sheet, holdingsaid sheets in spiral wound condition against substantial unwinding ofthe spiral during the vibration step hereafter, placing one spiral faceof said flow element on a vibrating plate for vibrating said flowelement along the axis of said spiral for axially aligning said sheetsand for controlling the shape of said flow passageways by movementbetween said sheets on the peaks and valleys of the corrugations,axially aligning said sheets and controlling the shape of thepassageways of the flow element by vibrating said flow element along theaxis of said spiral to cause relative movement between said sheets onthe peaks and valleys of the corrugations, and bonding said sheetstogether to give said flow passageways thereof substantially equal sizeand dimensional rigidity.

2. A method of making a laminar flow element, comprising uniformlycorrugating one sheet by a crimping roll, superimposing in contactanother sheet substantially coextensive with said one sheet of materialto provide a first sheet of planar material and a second sheet ofuniformly corrugated material having uniformly shaped and spacedcorrugations, spirally winding said superimposed sheets by a uniformwinding tension into a laminar flow element with the generating elementsof the corrugations extending parallel to each other and to the axis ofsaid spiral with a flow passageway located between each corrugation andsaid first sheet, and securing the corrugation peaks and valleys of saidsecond sheet at contact to said first sheet to give said flow elementits spiral shape and each flow passageway thereof dimensional rigiditywith each flow passageway being of substantially equal hydraulicdiameter and being substantially unobstructed, said sheets being of thesame metallic material, said securing step comprising joining by heatfusion the corrugation peaks and valleys at contact to said first sheetby heating said flow element in a furnace to at least the eutectictemperature near the melting point of the material so as to fuse thematerial of said sheets at said contacts by molecular fusion of only thematerial in said sheets to give said flow element its spiral shape andeach flow passageway thereof dimensional rigidity with each flowpassageway being of substantially equal hydraulic diameter and beingsubstantially unobstructed.

3. A method of making a laminar flow element, comprising superimposingin contact two substantially coextensive full temper thin sheets ofmetallic material comprising a first sheet of planar material and asecond sheet of uniformly corrugated material having uniformly shapedand spaced corrugations, spirally winding said superimposed sheets by auniform winding tension into a laminar flow element with the generatingelements of the corrugations extending parallel to each other and to theaxis of said spiral with a flow passageway located between eachcorrugation and said first sheet, telescopically assembling said sheetsinto a rigid cylindrical bore of a metallic casing, permitting saidspiral-sheets to expand to fill uniformly said bore, placing one spiralface of said flow element on a vibrating plate for vibrating said flowelement along the axis of said spiral for axially aligning said sheetsand for controlling the shape of said flow passageways by movementbetween said sheets on the peaks and valleys of the corrugations,axially aligning said sheets and controlling the shape of thepassageways of the flow element by vibrating said flow element along theaxis of said spiral, and heating said flow element to relieve thestresses in the corrugations radially and circumferentially of saidspiral and in said spirally wound sheet and to secure by heat fusionsaid sheets to said casing and to secure by heat fusion substantiallyall of the corrugation peaks and valleys of said second sheet at contactto said first sheet by heating said fiow element in a furnace to givesaid flow element its spiral shape and each flow passageway thereofdimensional rigidity with each flow passageway being of substantiallyequal hydraulic diameter and being substantially unobstructed.

4. A method of making a laminar flow element, as set forth in claim 3,with the step of selecting as the metallic material in both of saidsheets full temper thin sheets of steel, whereby corrugations are easilyformed in said second sheet, said sheets are easily spirally wound, areextremely thin so that the flow element approaches the desired porosity,permit use of small hydraulic radii, and have dimensional stability; andthe step of uniformly corrugating said second sheet by a crimping rollbefore superimposing said sheets.

References Cited in the file of this patent UNITED STATES PATENTS1,759,239 Morrison May 20, 1930 1,806,738 Burns et al. May 26, 19311,913,860 Spink June 13, 1933 2,212,186 Ricardo et a1 Aug. 20, 19402,445,766 erby et al. July 27, 1948 2,457,420 Veeder Dec. 28, 19482,721,952 Kenyon Oct. 25, 1955 2,752,672 Tolman July 3, 1956 2,768,431Hughes Oct. 30, 1956 2,824,364 Bovenkerk Feb. 25, 1958 2,833,027 FosterMay 6, 1958 2,890,885 Harvey June 16, 1959 2,944,504 Herman et a1. July12, 1960 FOREIGN PATENTS 9,228 Great Britain 1911 UNITED STATES PATENTOFFICE CERTIFICATE OF CORRECTION Patent No. 3 123,900 March 10, 1964Gordon H., Millar It is hereby certified that error appears in the abovenumbered patent requiring correction and that the said Letters Patentshould read as corrected below.

In the grant (only), line 1 for "Gordon H., Miller" read Gordon H Millerin the grant lines 2 andil2 and-in the heading to the printedspecification line 5 for "Instrumentsfl each occurrence, read Instrumentcolumn 3 line 43, for "directed" read directly column 4' line 49 for"axis 10" read axis 10d column 8, line 66 after "difference" insert indensity u Signed and sealed this 21st day of July 1964,

(SEAL) Attest:

ESTUN G, JOHNSON EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

1. A METHOD OF MAKING A LAMINAR FLOW ELEMENT, COMPRISING SUPERIMPOSINGIN CONTACT TWO SUBSTANTIALLY COEXTENSIVE SHEETS OF METAL COMPRISING AFIRST SHEET OF PLANAR METAL AND A SECOND SHEET OF UNIFORMLY CORRUGATEDMETAL, SPIRALLY WINDING SAID SUPERIMPOSED SHEETS INTO LAMINAR FLOWELEMENT WITH THE GENERATING ELEMENTS OF THE CORRUGATIONS EXTENDINGPARALLEL TO EACH OTHER AND TO THE AXIS OF SAID SPIRAL WITH A FLOWPASSAGEWAY LOCATED BETWEEN EACH CORRUGATION AND SAID FIRST SHEET,HOLDING SAID SHEETS IN SPIRAL WOUND CONDITION AGAINST SUBSTANTIALUNWINDING OF THE SPIRAL DURING THE VIBRATION STEP HEREAFTER, PLACING ONESPIRAL FACE OF SAID FLOW ELEMENT ON A VIBRATING PLATE FOR VIBRATING SAIDFLOW ELEMENT ALONG THE AXIS OF SAID SPIRAL FOR AXIALLY ALIGNING SAIDSHEETS AND FOR CONTROLLING THE SHAPE OF SAID FLOW PASSAGEWAYS BYMOVEMENT BETWEEN SAID SHEETS ON THE PEAKS AND VALLEYS OF THECORRUGATIONS, AXIALLY ALIGNING SAID SHEETS AND CONTROLLING THE SHAPE OFTHE PASSAGEWAYS OF THE FLOW ELEMENT BY VIBRATING SAID FLOW ELEMENT ALONGTHE AXIS OF SAID SPIRAL TO CAUSE RELATIVE MOVEMENT BETWEEN SAID SHEETSON THE PEAKS AND VALLEYS OF THE CORRUGATIONS, AND BONDING SAID SHEETSTOGETHER TO GIVE SAID FLOW PASSAGEWAYS THEREOF SUBSTANTIALLY EQUAL SIZEAND DIMENSIONAL RIGIDITY.